In many communication systems, for example in mobile communication networks, a plurality of devices shares resources on a common medium for transmission. One option of avoiding resource conflicts is to perform a scheduling or allocation of resources to selected devices while other devices are not allowed to use the same resources. Dynamic allocation of the resources during operation of the communication network can significantly increase the transmission efficiency so that the resources are not left unused if some of the devices have presently no or only a small amount of data to transmit while others require more resources. Dynamic allocation is particularly suitable if a single instance controlling the allocation is in communication with the plurality of devices sharing the medium. An example are user equipments in a cell or another area of a wireless communication system being controlled by a radio base station or a radio network controller.
Dynamic allocations are simplified if the resources are subdivided into resource blocks which can be allocated individually or in groups. Depending on the transmission technology, a resource block can for example be defined by a frequency range and a time interval in which a device is allowed to transmit data.
One example is the uplink transmission in LTE (Long Term Evolution) of the Universal Mobile Telecommunications System which is based on DFT-spread OFDM (Direct Fourier Transform spread Orthogonal Frequency Division Multiplexing), often referred to as Single Carrier Frequency Division Multiple Access (SC-FDMA). The LTE uplink is divided into resource blocks in time and frequency dimension as shown in FIG. 1. In the time dimension, subframes can be subdivided into two slots each as illustrated by their subdivision in the figure. In the frequency dimension, more than one resource block may be simultaneously allocated to one user, e.g. to user #2 having 3 allocated resource blocks in the example. LTE systems use a single carrier property which means that resource blocks allocated to a user equipment are consecutive in the frequency dimension.
In LTE, the uplink Resource Blocks (RB) are dedicated to users by means of uplink scheduling grants (SG) being transmitted on the Physical Downlink Control Channel (PDCCH). The uplink grants are addressed to the Cell-Radio Network Temporary Identifier (C-RNTI) of the user equipments. More details about this procedure can be found in Technical Specification 3GPP TS 36.321 V8.5.0 (2009-03) of the 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification.
For initiating a transmission, a user equipment (UE) 20 first requests uplink resources by transmitting a Scheduling Request (SR) 22 as illustrated in FIG. 2. In LTE this can be done using the Physical Uplink Control Channel (PUCCH).
The radio network, e.g. the eNB (Evolved Node B) 24 controlling the cell where the user equipment is located, selects the resource blocks to be allocated to the user and can select also the uplink transport format, defining parameters associated with the uplink transmission, like e.g. transport block size, physical layer coding, and modulation.
In this way, the eNB 24 performs uplink link adaptation and is aware of the format of the uplink (UL) transmission before it is received. A benefit of this procedure is that no uplink physical control channel is required to carry the information in contrast e.g. to TFCI (Transport Format Combination Identifier) signaling in WCDMA (Wideband Code Division Multiple Access). This reduces the uplink control signaling and improves coverage. In reply to the SR 22 the radio network represented by the eNB 24 in FIG. 2 sends a scheduling grant (SG) 26 indicating the selected RB. When the UE has received the SG it can start uplink data transmission 28 on the allocated uplink resources.
Despite the benefits of dynamic allocations as illustrated by the LTE uplink access scheme, there exist drawbacks. The scheduling request and scheduling grant before a transmission increase both the latency and signaling overhead in the communication system and thus reduce the transmission efficiency.